The present invention relates to a pressure sensor unit for a vehicle brake system, including a housing (2) in which at least one sensor element (1) is arranged which includes a deformation body (6) and at least one sensor means (7) arranged on the deformation body (6) for sensing a deformation of the deformation body (6).
Measuring the vacuum in a pneumatic brake booster is typically executed using an externally fitted sensor. The sensor is coupled to the interior of the brake booster by means of a connecting piece. Depending on the respective design, the pressure is measured in only one chamber or in both chambers of the brake booster.
WO 02/098718 A1 discloses a vacuum brake booster of a vehicle brake system with a sensor unit for sensing pressures, with the sensor unit including two sensor elements in one common housing.
Prior art pressure sensors typically comprise a pressurizable deformation body, in most cases one deformable diaphragm or pressure measuring plate which is possibly arranged on a base member, as well as a sensor means arranged of the deformation body, which determines the pressure-responsive displacement or deformation of the deformation body. The sensor means can be based on a capacitive or resistive measuring principle.
When the sensor means is designed as a capacitor structure (capacitive measuring principle), at least one electrically conductive measuring electrode is disposed in the area of the diaphragm surface so that it is moved by the deformable diaphragm surface. In addition, a back plate electrode is provided which is attached to the base member and along with the measuring electrode forms a capacitor. The pressurization alters the displacement of the diaphragm and, thus, the distance of the capacitor plates. The change in capacity entailed can be taken into account as an indicator of the pressure. For example, capacitive sensors made of ceramics are used which are fitted to a housing by means of ring seals and are this way sealed against the medium of measurement.
When the sensor means is designed with pressure-sensitive resistors (resistive measuring principle), resistive structures are fitted on the diaphragm (on the deformation body), and the resistance value depends on the deformation or flexure of the diaphragm and, thus, is also an indicator of the pressure applied. The deformation bodies employed are made of ceramics or metal. Document DE 102 52 023 B3 discloses a pressure sensor which has a plastic deformation body that can be made by injection molding, for example.
Monolithic, piezoresistive dies (structures) are frequently employed, which are fitted to a ceramic base using an elastic adhesive with silicon. A boron silicate glass is frequently interposed between the piezoresistive structure and the ceramic base in addition. The measuring pressure is then introduced from below through a hole in the ceramic base (and, if provided, in the boron silicate glass) to the electrically inactive surface of the sensor. The top side of the sensor element must be protected against dirt and vibrations by way of a sealing compound likewise containing silicon.
The use of silicon in the area of the brake booster is undesirable for various reasons. For example, silicon impairs the conductivity of contact surfaces, what can cause malfunctions of the brake booster.
Prior art pressure sensor units, as disclosed in the document DE 196 37 763, for example, generally comprise a housing with a supply opening for the pressure medium, the pressure of which must be determined. The housing of the sensor unit is connected to the system to be monitored e.g. by a thread or other means of attachment. The pressure medium is supplied through the supply opening to the sensor element arranged in or at the housing. In this case, the sensor element is required to be pressure-tightly coupled to the housing or the ceramic base. As is known, this is executed by gluing with an elastic adhesive which contains silicon, or by a press fit, e.g. using a spring, and with simultaneous sealing by means of a sealing material, e.g. a ring seal.
Based on the above state of the art, the invention has for its object to provide an improved pressure sensor unit, which exhibits a simple and cost effective and, additionally, pressure-tight, durable and especially non-silicon connection between housing and sensor element.